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THE INSTITUTE OF INDUSTRIAL RESEARCH 



THE PRESERVATION 

OF THE 

EXTERIOR OF WOODEN BUILDINGS 



BY 



ALLERTON S. CUSHMAN, Director 

J-HE INSTITUTE OF INDUSTRIAL RESEARCH 
AND 

HENRY A. GARDNER, Asst. Director 

IN CHARaE DIVISION OF PAINT TECHNOLOGY, 
THE INSTITUTE OP mOUSTRIAL RESEARCH 




WASHINGTON 

1911 



THE INSTITUTE OF INDUSTRIAL RESEARCH 



Allerton S. Cushman, A. M., Ph. D., Director, In Charge Division Metallurgical 

Problems. . 

Henry A. Gardner, Assistant Director, In Charge Division of Paint Technology. 
N. Monroe Hopkins, Ph. I)., In Charge Division of Electrical Engineering and 

Electrochemistry. 
Chas. a. Crampton, M. D., Ph. G., In Charge Division of Food and Drug 

Products. 
G. W. CoGGESHALi/, Ph. D,, Jn Charge Division of Mill Problems. 
Chas. Backer ville, Ph. D., F. 0. S., In Charge Technology of the Rarer Elements, 



Gjpyrjght, 191 1, The Institute of Industrial Research 



THE INSTITUTE OF INDUSTRIAL RESEARCH 



THE PRESERVATION 

OF THE 

EXTERIOR OF WOODEN BUILDINGS 



BV 

ALLERTON S. CUSHMAN, Director 

THE INSTITUTE OF IN'KUSTRIAL RESEARCH 

AND 

HENRY A. GARDNER, Asst. Director 

IN CHARGE DIVISION OF PAINT TECHNOLOGY, 
THE INSTITUTE OF INDUSTRIAL RESEARCH 




WASHINGTON 

1911 



WASHINGTON, D. C. 
PRESS OF JUDD & DETWEILER, INC. 

igri 



*CI.A2S698«5 



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PREFACE. 



For a number of years the writers have been making a 
study of industrial problems and have been publishing the 
information which they have acquired, regarding the value 
of various structural materials, for the benefit of consumers 
as well as producers. The Institute of Industrial Research 
has received so many requests recently for information in 
regard to just what paints should be selected for the protec- 
tion and decoration of houses and other buildings that It 
has seemed best to sum up the subject in the form of a spe- 
cial pamphlet or bulletin. It is only after years of investi- 
gation work carried on by the authors, both separately and 
in co-operation, that any review of the work has seemed 
possible, for only recently have the results of tests carried 
on in a number of different localities seemed to justify a defi- 
nite opinion in regard to the best selection of exterior paints. 
No attack on any one paint material is here included, but the 
value of each has been carefully weighed, and the attempt 
is made to discuss them in the light of experience and knowK 
edge. It is the authors' intention in this bulletin to put intb 
the hands of architects and paint users who may not be thor- 
oughly familiar with the technical properties of paint mate- 
rials, information which will enable them to make a proper 
and intelligent selection of paints for the preservation and 
decoration of the exterior of wooden buildings. 



The Preservation of the Exterior of Wooden Buildings 



Lumber and its Relation to Paints: The proper choice 
and treatment of lumber is one of the most important prob- 
lems which the builder as well as the painter has to face. 
When about to build a dwelling, barn, or other structure 
made principally of wood, the question is sure to arise in 
regard to what variety to select so as to get the maximum 
service and money value. The locality in which the struc- 
ture is to be built must often have a bearing upon this ques- 
tion. While it is true that the painting of each type of wood 
demands the special consideration of the painter, it is also 
true that the study of paints for wood protection points 
toward the production of a paint that will give satisfactory 
results under all conditions and on all grades. It is the 
writers' opinion that a paint may be made that will be per- 
fectly well suited for the preservation of every species of 
wood, provided the paint is properly treated in the hands of 
the skillful and intelligent painter, who can produce lasting 
results on almost every type by varying the proportion of 
thinners and oil in the various coats. The painter who uses 
the same paint on soft pine, and again on hard pine, without 
making a special study of how to reduce the priming coat 
for the hard pine, will be likely to get inferior results on the 
latter. In case of failure, the natural impulse is often to 
place the blame upon the paint, whereas the real responsibil- 
ity may rest upon the painter's lack of knowledge. 

Signs of Paint Failure: Those who are responsible for 
the care and maintenance of property are familiar with the 
condition of surface presented by almost all wooden build- 
ings or structures which have been improperly painted with 

Note. — For a more detailed account of the lumber question, see "Modern 
Lumber as a Problem for the Painter," read by John Dewar, at the Con- 
vention of Master House Painters' and Decorators' Association of Penn- 
sylvania, January, igii, Pittsburg, Pa. 

4 



Photographs Showing Different Forms of 

Decay Exhibited by Improperly 

Made Paints 



Inferior paints. "Chalking" or "flouring" are terms used 
to describe the condition of a paint surface which has de- 
teriorated within the paint film. The formation of minute 
fissures, generally spoken of as "checking," as well as the 
effects best described as cracking, scaling, peeling, and blis- 
tering, are other signs of failure which cause paint coatings 
to present an unsightly appearance, and which point inev- 
itably either to the use of improperly made paints or to 
improper application. The cause of these conditions is 
not difficult to understand when even a brief study of the 
character of the materials entering into the composition of 
a paint has been made. It is, however, a fortunate circum- 
stance that the proper admixture of different types of pig- 
ments enables us to correct the strong tendency exhibited by 
special pigments to rapidly deteriorate in an oil film. This 
point will be more fully discussed in a later paragraph. 

Requisites of a Good Paint: Progressive manufacturers 
are aiming to produce a paint which will show, under the 
widest range of conditions, good hiding power, adhesive- 
ness, freedom from internal strains, permanency of color, 
relatively high imperviousness to moisture, sufficient elas- 
ticity to prevent scaling or cracking when subjected to ex- 
pansion or contraction, and freedom from the chemical 
action which results in deep checking or excessive chalking. 
Such a product as this cannot be attained, in the writers' 
opinion, by the use of any one pigment in linseed oil. In 
order to meet all the demands as stated above, there should 
be in an economical and durable paint a proper percentage 
of the various pigments which, united, will tend to correct 
each other's faults, and thus produce a durable paint coating 
of maximum efficiency. 



• The Composition of Paints: As is well known, a paint is 
a mixture of one or more pigments and a vehicle which acts 
the part of the spreading and binding medium. Up to the 
present time the vehicle portion of paints has generally been 
made of linseed oil, admixed with some volatile thinner, 
such as turpentine. The subject of oils and paint vehicles 
will be discussed more fully later on. 

Physical Properties of Pigments: The pigment portion 
of a paint for use on barns and farm buildings may, if de- 
sired, be composed of properly selected iron oxides or other 
colored pigments, even containing in some cases a moderately 
high percentage of silica, clay, or other inert materials, and 
give perfectly satisfactory results. For the preservation and 
decoration of dwellings, however, the pigment portion of 
paints is generally made as a whole or in part of the more 
expensive white pigments, such as white lead and zinc oxide. 
The relative values and properties of these white base pig- 
ments will now be taken up. 

White Leads: White lead, either of the corroded or sub- 
limed type, is perhaps the most generally used of all the 
white pigments as a paint base. Corroded white lead is a 
basic carbonate of lead, while sublimed white lead is a basic 
sulphate of the same metal. Both of these types are white, 
and admirably adapted as painting materials. They take 
relatively the same amount of oil and spread easily, produc- 
ing paint films which are highly opaque and which, there- 
fore, hide efficiently the surface upon which they are placed. 
Sublimed white lead is a relatively finer pigment than cor- 
roded white lead, and seems to show a tendency to chalk 
to a greater extent upon exposure to the weather. Cor- 
roded white lead is more alkaline, however, than sublimed 

G 



white lead, and when used alone with linseed oil generally 
shows a tendency to chalk to a considerable extent in a short 
time and to show deep checking, thus permitting the admis- 
sion of moisture. The alkaline nature of this pigment pro- 
duces considerable action upon certain tinting colors and 
results in fading or darkening, when mixed with delicate 
greens or blues. 

The use of white lead has been condemned in some parts 
of this country as well as abroad, because of its alleged 
poisonous properties. While it is true that lead poisoning 
may occasionally occur in some factories where the workman 
and his conditions are not properly safeguarded, it is, never- 
theless, a fact that lead poisoning very seldom occurs among 
painters of experience and cleanly habits. Carelessness in 
mixing white lead is, fortunately, a practice almost obsolete 
among modern painters. The use of paints already ground 
in oil by means of machinery to a pasty condition, allowing 
easy working and reducing, obviates the danger of lead 
poisoning from any such cause as this, even though the per- 
centage of lead in such paints is in preponderance. Recent 
efforts that have been made by the legislatures of certain 
States to brand lead paints as poisonous are not only unnec- 
sary, but show a complete ignorance of the problem. 

Zinc Pigmetits: Another pigment which has proved itself 
of great value to the painter is zinc oxide. The use of this 
pigment may be said to have almost revolutionized the paint 
industry of the world, and its increased consumption during 
the last ten years is sufficient evidence of its value as a paint- 
ing material. Zinc oxide is produced by oxidation and sub- 
limation of zinc ores and is not only extremely fine, but of 
great whiteness. It has good hiding power, although not 
quite so great as that shown by the white leads. It tends to 



produce a glossy surface, making it especially valuable for 
use on interior work and in enamels. When used alone it 
has the effect of hardening the oil film in which it is envel- 
oped, and upon long exposure causes cracking and scaling. 
However, when the sublimed or corroded white leads are 
properly combined with zinc oxide, a more durable surface 
is produced, the shortcomings of each pigment being over- 
balanced by the good properties of the other. The proper 
combining properties of zinc oxide with white lead may be 
said to vary between 20 to 55 per cent of zinc oxide for 
paints designed for exterior use. In the opinion of the au- 
thors, lead and zinc pigments in the above percentage, prop- 
erly blended and ground, make paints of far better wearing 
value than can be produced with either white lead or zinc 
oxide used alone.. 

Zinc Lead: Zinc lead, a pigment sublimed from mixed 
lead and zinc ores and containing about equal proportions of 
zinc oxide and lead sulphate intimately combined, as well as 
leaded zinc, a produce similarly produced, but with the zinc 
oxide running about 75 per cent, are white base pigments of 
value, which are used to a considerable extent. They arc 
generally slightly off color, however, and are therefore used 
most largely in paints which are to be tinted in various 
colors. 

Lithopone: Lithopone, a pigment produced by precipita- 
tion, and consisting of zinc sulphide and barium sulphate, is 
of great value in the manufacture of interior paints. On ac- 
count of its liability to darken and disintegrate, however, it 
is seldom used on exterior work, although recent tests have 
shown that when used in combination with zinc oxide and 
whiting, it gives very promising results. 



Crystalline Pigments and Their Use: Barytes (barium 
sulphate), silex (silica), whiting (calcium carbonate), gyp- 
sum (calcium sulphate), asbestine (silicate of magnesia), 
and China clay (silicate of alumina) are white crystalline 
pigments which, when ground in oil, become transparent. 
All of these pigments possess the property of strengthening 
a paint film made of white lead and zinc oxide, and often 
increase the durability of such a paint. Barytes, silica, and 
China clay are especially valuable for this purpose. Asbes- 
tine, because of its needle-like structure and low gravity, pre- 
vents settling and acts as a reinforcer of paint films. Whit- 
ing or calcium carbonate should be used when zinc oxide is 
in excess in a paint, so that the hardness of the paint may be 
overcome. 

A white paint must be possessed of sufficient opacity to 
efficiently hide the surface upon which it is placed, when 
three coats are applied for new work or two coats for re- 
painting work. Mixtures of the white leads and zinc oxide, 
with the latter pigment running not over 55 per cent, will 
easily produce such a result and wear well. It Is generally 
deemed advisable, hov/ever, by most manufacturers to take 
advantage of the excessive opacity of such mixtures, which 
allows the introduction of moderate percentages of those 
inert pigments which give greater strength and other desira- 
ble features to a paint. The percentage of natural crystal- 
line inert pigments to add to a white paint made of lead and 
zinc must, however, be moderate and insufficient to detract 
materially from the hiding power of the paint. 

Nqye. — Pigments such as silica, barytes, china clay, and asbestine are 
thoroughly inert. Recent investigations have proved that they accelerate 
the drying of linseed oil, but this is not due to any chemical action they 
exert, but rather to their physical action in distributing the mass of oil in 



which Ihey are ground, and thus allowing a greater surface to be exposed 
to the oxygen of the air. 

It is also possible that some of the inert pigments may stimulate oxida- 
tion l:)y catalytic or contact action, although they are not chemically active 
in themselves. 

JVhite-Paint Formulas : From these conclusions which 
have come from wide experience in the testing of paints 
under actual service conditions, there can be recommended 
to the buyer of paints and to the manufacturer and master 
painter those machine-mixed paints in white, made by repu- 
table manufacturers, the composition of which will show a 
mixture of white lead and zinc oxide, with the latter pigment 
within limits of between 15 to 55 per cent, and especially the 
same mixtures reinforced with the moderate percentage of 
crystalline inert pigments referred to above. 

Tinted paints possess greater hiding power than white 
paints, and the above proportions would be somewha; 
changed for a tinted paint containing any percentage of 
coloring material. Tinted paints are, moreover, far more 
serviceable than white paints, as will be shown later. 

MUl vs. Paddle: The mixtures under consideration should 
be ground in linseed oil by the manufacturer, through stone 
or steel mills, to a very fine condition, as it is only through 
proper grinding that the pigments can be properly blended. 
The mixing of paint by hand is, fortunately, to a large ex- 
tent a thing of the past. The uneven lumping of hand- 
mixed paints are often the cause of their failure. Such an- 
cient and crude practice should be avoided by every painter, 
for it is more economical to obtain semi-paste paints, prop- 
erly ground by machinery, to such a condition that they may 
be easily broken up and tempered. Such paints may be re- 

10 



duced to the proper consistency with oil and volatile thinner 
for application to any kind of wood. 

In the opinion of the writers, a majority of the paints 
sold by reputable ciealers and made by reputable manu- 
facturers in this country are not only made from the 
best linseed oil and highest-grade pigments obtainable, but 
are put up in a form ready for the painter to thin down with 
full oil or turpentine reductions, either for priming work 
or to be used without reductions for finishing coats. The 
large metropolitan painter who wishes to make his own tints 
and shades may, however, prefer to have his mixed pigment 
paint ground by the manufacturer in heavy paste form for 
certain purposes. 

Results of Field Tests: A careful analysis of the results 
of field tests which have been carried on in different parts of 
the country would be far too voluminous for insertion in 
this bulletin. The official findings of special committees of 
inspection have already been published in special reports. 
Whereas there may still remain ground for some difference 
of opinion in regard to the interpretation of the results ob- 
tained on the various test fences, there can be no doubt that 
considerable information of the highest value has been 
yielded, both to the producers and consumers of paints. 
One of the principal results obtained from these tests has 
led to the opinion expressed above by the writers, that better 
results can be obtained by a proper mixture of selected pig- 
ments than by the use of any one pigment in linseed oil. 
This conclusion has also been reached by engineers of the 
United States navy, and, as a result, the specifications of the 
Bureau of Yards and Docks for paints made of straight white 
lead and oil have recently been changed to call for white lead 

11 



combined with upwards of 50 per cent of zinc oxide. Many 
engineers and master painters have interpreted the results of 
the tests in the same way, and the attention of the authors 
has been called to a number of opinions which show that the 
tendency of demand among those who are properly informed 
is for a high-grade combination type of paint rather than for 
any single pigment paint. 

Color: The selection of the color for a dwelling or other 
structure is a matter that depends largely upon the good 
judgment and taste of the owner, combined with the advice 
of the painter. One point, however, should be impressed 
upon the mind of both, namely, that practically all 

SHADES OR TINTS MADE UPON A GOOD WHITE PAINT BASE, 
THROUGH THE USE OF PERMANENT TINTING COLORS, WILL 
BETTER WITHSTAND EXPOSURE TO THE ATMOSPHERE THAN 

THE WHITE BASE USED ALONE. Owing to the cheerful 
effect produced by the use of white paint on dwellings, a 
very large quantity of white will continue to be used. If 
these white paints are designed in line with the suggestions 
brought out above — that is to say, if the white lead bases 
are properly reinforced with zinc oxide and other pigment- 
ary materials — better results will undoubtedly be obtained, 
as far as appearance and durability is concerned, than if 
white lead had been used alone. The consumer should re- 
member, however, that more durable results will be obtained 
by the use of tinted paints. 

Reductions and Thinners: Turpentine, with its sweet 
odor, high solvent action, and wonderful oxidizing value, 
has always taken first place among the volatile liquids used 
for thinning paints. Wood turpentines, produced from the 

steam distillation of fine-cut fat pinewood or from the de- 

12 



structive distillation of stumpage and sawdust, have been 
refined In some cases, by elimination of odor and toxic effects, 
to such purity that they are equally as good as the purest 
grades of gum turpentine, and their use is bound to Increase 
In the paint industry. 

The painter and manufacturer have come to understand 
that certain grades of asphaltum and paraffine distillates are 
equally as satisfactory as turpentine for use in paints for ex- 
terior purposes. Those volatile oils which are distilled 
from crude oil with either a paraffine or asphaltum base and 
possessed of boiling point, flash point, color, and evapo- 
rative value approximating similar constants of turpentine, 
are excellently suited to partly, and In some cases wholly, 
replace turpentine In exterior paints. A little additional 
drier added to paints thinned with these materials will cause 
oxidation to take place In the proper time. 

Prominent master painters* have shown that benzol, a 
product obtained from the distillation of coal tar, differing 
from benzine, a product obtained from the distillation of 
petroleum, is a valuable thinner to use in the reduction of 
paints for the priming of resinous lumber such as cypress 
and yellow pitch pine. The penetrating and solvent 
value of benzol is high, and it often furnishes a unison be- 
tween paint and wood that Is a prime foundation to subse- 
quent coatings, preventing the usual scaling and sap exuda- 
tions, which often appear on a painted surface. Because of 
the great solvent action of benzol, however, this material 
should never be used In the second and third coatings. These 
facts will doubtless interest the Southern painter, who has so 
much wood of a refractory nature to paint. 



* Dewar, Titzel et al. 

13 



WAy i% 191, 



Oils: The increasing cost of linseed oil has raised the in- 
teresting question as to whether or not it is good practice to 
use an admixture of other oils in connection with it, in high 
grade paint coatings. Strong differences of opinion will 
probably be found in regard to this question, and undoubt- 
edly further investigation work is necessary in order to decide 
it. A number of different oils have been proposed for the 
purpose, of which, perhaps, soya bean oil is the one which 
has been most prominently discussed. No definite formulas, 
however, should be recommended until the results of investi- 
gations which are now being carried on are in hand. A sys- 
tematic series of test panels is now being erected in Wash- 
ington, D. C, on the grounds of The Institute of Industrial 
Research, which are designed to gather data covering just 
this point. 

The flax crop conditions have been most discouraging 
during the past two years, and the natural shortage of seed 
has caused a rise in the price of linseed oil, which has neces- 
sitated a rise in the price of paint. The added protection to 
be secured, however, through the frequent application of 
paint far outweighs any increased cost which has been caused 
by the rise in price of the raw commodities entering into the 
composition of paint. 



14 . 



one copy^del. to tot. Div 



